1. Field of the Invention
This invention relates to an image signal processing apparatus, an image signal processing method and a program, and more particularly to an image signal processing apparatus, an image signal processing method and a program suitable for use for conversion of an interlaced signal into a progressive signal.
2. Description of the Related Art
In order to enhance the picture quality (by removal of line flickering and so forth) of an image to be displayed on a display unit of a television receiver or the like, an IP conversion process is used. The IP conversion process converts an image signal of the interlaced type (a signal of the type described is hereinafter referred to as interlaced signal) into another image signal of the progressive type (a signal of the type described is hereinafter referred to as progressive signal). The IP conversion process has been popularized as a technique for a fixed pixel display unit such as a liquid crystal display unit or a plasma display unit. In the following, a television system is described taking the NTSC (National Television System Committee) system as an example.
The IP conversion process can be implemented by various methods in response to the type of an interlaced signal prior to the IP conversion including 2·3 pull-down inverse conversion, 2·2 pull-down inverse conversion, motion adaptive IP conversion and motion compensated IP conversion.
In order to convert an interlaced signal of film material, the 2·3 pull-down inverse conversion or the 2·2 pull-down inverse conversion is applied. The film material here is obtained by conversion of material produced by picking up 24 or 30 images per second using a film camera which is used for image pickup, for example, for a movie into an interlaced signal of 60 images per second by 3·2 pull-down telecine conversion or 2·2 pull-down telecine conversion by means of a telecine apparatus. A progressive signal which is a result of IP conversion by the 2·3 pull-down inverse conversion or the 2·2 pull-down inverse conversion includes reproduced original images of the film material before the telecine conversion and does not give rise to generation of line flickering when it is reproduced.
On the other hand, in order to IP convert an interlaced signal of video material, the motion adaptive IP conversion or the motion compensated IP conversion is suitably applied. The video material is obtained by picking up images in accordance with the interlaced system using a video camera.
In the motion adaptive IP conversion, where pixels in each even-numbered (odd-numbered) line to be interpolated in each odd-numbered (even-numbered) field do not involve any motion (any temporal variation), those pixels which exist in even-numbered (odd-numbered) lines of a pair of even-numbered (odd-numbered) fields preceding and succeeding the odd-numbered (even-numbered) field are used to perform the interpolation. On the other hand, where the pixels in each even-numbered (odd-numbered) line to be interpolated in each odd-numbered (even-numbered) field involve some motion (some temporal variation), those pixels which exist in the odd-numbered (even-numbered) line in the odd-numbered (even-numbered) field are used to perform interpolation.
With the motion adaptive IP conversion, line flickering is removed from a still picture which does not include any motion, but even with an image which includes motion, line flickering is reduced when compared with an alternative case wherein IP conversion suitable for the film material is applied.
Therefore, such a countermeasure as described just below is taken popularly. In particular, it is first decided whether an interlaced signal before IP conversion is performed is of film material or video material. Then, either a progressive signal for which the IP conversion for film material is applied or another progressive signal for which the IP conversion for video material is applied is outputted based on a result of the decision. The countermeasure is disclosed, for example, in Japanese Patent Laid-Open No. 2004-96223.